Skylights are used to illuminate buildings in a pleasing and energy-conserving way. Tubular skylights such as those made by the present assignee typically have a roof-mounted transparent cover or dome, a light conveying tube assembly extending down from the dome into the building to a ceiling, and a light diffuser plate covering the bottom of the tube at the ceiling. An example of a commercially successful tubular skylight is disclosed in U.S. Pat. No. 5,099,622, assigned to the same assignee as the present invention and incorporated herein by reference. Other patents owned by the present assignee that pertain to various skylight technologies are disclosed in U.S. Pat. Nos. RE36,496 (dome with reflector), 6,219,977 (round-to-square adapter), and 5,896,712 (dome with circular grooves), all of which are incorporated herein by reference.
As recognized herein, a difficult goal of skylight design is the provision of as constant a light output as possible regardless of the time of day. This is difficult to achieve because in the mornings and evenings the sun is at a low angle and less light enters the skylight than at midday, when the sun is at a high angle. Indeed, in designing a skylight to maximize light collection and throughput during the morning and evenings hours, the resulting skylight can over-illuminate a room at midday, with so-called “hotspots” (areas in the room where light from the skylight undesirably might be focused) being particularly noticeable at midday. Thus, the present invention recognizes the desirability of achieving a more constant light output regardless of time of day, as well as the desirability of mixing light sufficiently as it propagates down the tube into the room to avoid “hotspots”. With these critical recognitions in mind, the invention herein is provided.